It is known that silver ions strongly inhibit the growth of bacteria and other microorganisms. Silver ions destroy important cell components of microorganisms, so that their vital functions do not work anymore. Silver shows a broad-spectrum antibacterial activity and is even efficient against antibiotic-resistant strains. Moreover, silver targets numerous sites within the bacterial cell, thus decreasing the chance for the bacteria to develop any kind of resistance.
With increasing resistance of most of the pathogen germs against the usually used antibiotics, silver was recently rediscovered as an antibacterial active substance. In fact, due to its disinfectant property, silver has long been used for hygienic and medicinal purposes.
For instance, silver compounds were major weapons against wound infection in World War I until the advent of antibiotics. In 1884 German obstetrician C.S.F. Crede introduced 1% silver nitrate as an eye solution for prevention of Gonococcal ophthalmia neonatorum, which is perhaps the first scientifically documented medical use of silver. Further, silver sulfadiazine cream was a standard antibacterial treatment for serious burn wounds and is still widely used in burns units.
Currently, many silver containing products are available on the market such as wound dressings, catheters and/or tumor prosthetic systems.
One known coating fabrication method is based on a vacuum coating method which offers reliable protection for the surfaces of medical implants against bacterial contamination. A pure silver coating is applied via a PVD (Physical Vapor Deposition) process followed by a silicon oxide coating deposited via a PECVD (Plasma Enhanced Chemical Vapor Deposition) process. The coating thickness is generally below 200 nm.
PVD and CVD processes usually require highly expensive coating systems. Further, they are also energy consuming due to the high vacuum requirements. Furthermore, the PVD technique is a “line-of-sight” technique, which means that complex surfaces would be very hard to coat homogeneously.
Moreover, irreversible pigmentation of the skin and/or the eye, i.e. argyria or argyrosis, due to possible “excessive” silver deposition, may develop after prolonged exposure to silver or silver compounds.
Besides, leukopenias and neuromuscular damages could be caused by increased silver concentrations. Allergic reactions were described in the literature. Past coating attempts with silver salts or elementary silver were reported to cause significant increases of silver concentrations in the serum of the concerned patients.
Accordingly, it is an object of the present invention to provide a medical device, for instance embodied as an implant, having a coating of advanced properties.
Preferably such a coating should be provided as an antibacterial coating, for instance on metallic implants.
In particular it should be possible to control or to adapt the antibacterial efficacy, for instance the leaching rate, of such a coating.
Preferably the ingrowth of human tissue and/or bone should be promoted by such a coating on an implant.
The fabrication of such a coating should be based on an easy and cost reduced concept.